This invention relates generally to the extraction of useful power from the sea, and more particularly to an underwater thermal energy conversion unit that exploits the difference between the surface temperature of a water body and its temperature at the depth of submersion.
It has been estimated that in the course of a year the sun pours 3600 quintillion BTU's of energy upon the earth and that roughly half of the incredible amount of energy that reaches the earth lands in the tropics. Since the tropics are largely composed of ocean, most of the solar energy is soaked up and stored in the surface water of the sea.
The idea of extracting useful power from ocean thermal differences is almost 100 years old, having first been conceptualized in 1881 by the French physicist d'Arsonval. One possible technique to tap solar energy stored in the sea is by setting stored heat alongside stored cold, the latter being derived from water pumped up from the cooler depths.
One arrangement accomplishing this purpose is characterized in a recent Business Week article as "A Jules Verne Scheme to Harness Ocean Heat." This arrangement makes use of a floating platform on which a turbine is mounted, the turbine being spun by vaporized ammonia that is turned back to liquid in a condenser chilled by cold sea water pumped up to the platform from a depth of 4000 feet. The liquefied ammonia flows back to an evaporator tank to repeat the cycle.
Another approach is that taken in the 1935 U.S. Pat. No. 2,006,985 to Claude et al. wherein the heat in the warm surface water of tropical seas is used to produce steam to drive a turbine. In the Claude et al. system, warm sea is pumped to an elevated tank which is maintained under sufficient vacuum by means of a barometric leg to cause the warm water to boil. The resultant low-pressure, low-density steam is passed to a power-generating turbine and then to a condenser in which the steam is liquefied by cold sea water pumped up from the depths of the sea. Thermal conversion techniques also involving the production of steam are also disclosed in the 1952 U.S. Pat. No. 2,595,164 to Nisolle and the 1976 U.S. Pat. No. 3,312,054 to Anderson.
The difficulty with schemes of the type heretofore proposed is that in all instances they involve relatively complex installations and require powered pumps or other mechanisms to bring a large volume of ocean-stored cold water alongside stored heat. And while many studies have been made regarding the possibilities of exploiting ocean thermal differences, and various projections have been made as to when in the distant future such installations will become a reality, the fact remains that there are no significant commercial installations based on existing schemes.